1. Field of the Invention
The present invention relates to emulsifiers for use in water-in-oil emulsions. More particularly, the present invention relates to the use of thermally altered lecithin as an emulsifier for water-in-oil emulsions and the stable water-in-oil emulsions prepared therewith.
2. Description of the Prior Art
An emulsion can be defined as a dispersion of one immiscible liquid in another, stabilized by a third component, the emulsifying agent. Emulsion systems, however, by their very nature are thermodynamically unstable. See, for example, Encyclopedia of Emulsion Technology, Vol. 2, pp. 159-170. This inherent problem of stability has often resulted in limited applications for many potentially useful emulsion systems. Stable, improved emulsion systems exhibiting good holding capacities are therefore ever in demand and on the forefront of development.
Lecithin is well known, particularly as a surfactant and/or as an emulsifier. Lecithin is obtained from natural sources such as egg yolk, and plants such as soybean, maize, rapeseed, and the like where it is a by-product of vegetable oil refinement. The composition of commercial lecithin depends on the source, methods of preparation, and degree of purification, but in the most pure form it is comprised of mainly phosphatides. For example, granular soybean lecithin may contain principally phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol and the like.
The literature is replete with references to the use of lecithin in various applications. For example, the applications include the use of lecithin in:
foodstuffs such as mayonnaise, sponge cake, confectioneries such as whipping cream and chocolate, dried dairy products such as powdered creams for coffee, and steam cooked noodles; PA1 cosmetics such as skin creams, shampoos and hair dressing agents; PA1 emulsions for producing doughs or batter for bakery products; PA1 pharmaceutical preparations, including acne preparations, antihemolytic emulsions, compositions for the treatment of bloat in ruminants, and carcinostatic drug compositions; PA1 non-stick cooking compositions used for coating cookware; PA1 vehicles for hard and soft gelatin capsules; PA1 polymer compositions, including polyester molding compositions, water soluble polyvinyl acetate films and a resin dispersion of an electrophotographer, as well as an asphalt emulsion for use in pavements; PA1 fungicide and pesticide dispersions; PA1 hydraulic fluids; and, PA1 emulsion explosive compositions. PA1 (i) a continuous oil phase, PA1 (ii) a discontinuous aqueous phase, and PA1 (iii) an emulsion stabilizing amount of a thermally altered lecithin composition which has been prepared by heating lecithin at a temperature in the range of from about 100.degree. C. to about 250.degree. C. for a period of time ranging from about 15 to about 480 minutes. Such water-in-oil emulsions have been found to exhibit excellent stabilizing and holding capacity. PA1 (i) heating lecithin at a temperature in the range of from about 100.degree. C. to about 250.degree. C. for a period of time ranging from about 15 to about 480 minutes, PA1 (ii) mixing the product of (i) with an oil, and PA1 (iii) adding to the product of (ii) an aqueous phase with agitation to thereby yield a water-in-oil emulsion; or, PA1 (i) heating lecithin in an oil at a temperature in the range of from about 100.degree. C. to about 250.degree. C. for a period of time ranging from about 15 to about 480 minutes, and PA1 (ii) adding to the product of (i) an aqueous phase with agitation to thereby yield a water-in-oil emulsion. These processes have been found to be simple yet effective in producing a stable water-in-oil emulsion. PA1 (i) heating lecithin at a temperature in the range of from about 100.degree. C. to about 250.degree. C. for a period of time ranging from about 15 to about 480 minutes, PA1 (ii) mixing the product of (i) with an oil, and PA1 (iii) adding to the product of (ii) an aqueous phase with agitation to thereby yield a water-in-oil emulsion. PA1 (i) heating lecithin in an oil at a temperature in the range of from about 100.degree. C. to about 250.degree. C. for a period of time ranging from about 15 to about 480 minutes, and PA1 (ii) adding to the product of (i) an aqueous phase with agitation to thereby yield a water-in-oil emulsion. In a most preferred embodiment with respect to the latter process, the product of step (i) is allowed to cool to a temperature below 100.degree. C. before the aqueous phase is added thereto, e.g., to preferably about 80.degree. C.
While lecithin is well-known as an emulsifier, it has been recognized as a somewhat inferior emulsifier, particularly for water-in-oil emulsions. The use of lecithin as an emulsifier is therefore generally most preferred in oil-in-water type emulsions, or with the lecithin, due to its being an inexpensive source, filling the role as a secondary emulsifier in the presence of a primary emulsifier.
For example, the use of lecithin in emulsion explosives, wherein water-in-oil emulsions are often used, is well-documented. A number of publications exemplify this application. These include U.S. Pat. Nos. 4,602,970, 4,507,161, 4,473,418, 4,308,081, 4,357,184, 4,555,278, British Pat. Nos. 2,179,338 and 2,037,269; European Patent Application No. 0155800 and Australian Patent No. 10510/83. In all of these publications, the lecithin employed is used as an emulsifier or surfactant, with the lecithin being normal lecithin such as soybean lecithin. Some of these publications, however, do suggest that the lecithin should be used as a secondary emulsifier, and/or that lecithin is basically an inferior emulsifier.
The chemical modification of lecithin is known in the art as one manner in which to improve the lecithin for many different applications. U.S. Pat. No. 4,479,977, for example, discusses the acylation of lecithins to provide a clear, heat resistant lecithin useful as a release agent. Hydrolyzed lecithins are disclosed as being useful surfactants or emulsifiers. U.S. Pat. No. 4,547,387 discloses a rearrangement reaction product of a lecithin to form a better anti-spattering agent for margarine. Japanese Patent Application No. 61-162148 discloses a method for preparing a creamy emulsified oil or fat composition containing a milk component by adding a modified lecithin thereto. The modified lecithin is selected from a phosphatidylcholine-rich fractionated lecithin, a phosphatidylethanolamine- and/or phosphatidylinositol-rich fractionated lecithin, a partially hydrolyzed lecithin in which part of the fatty acids are hydrolytically removed, an acetylated lecithin, and a lecithin modified by a combination of fractionation, hydrolysis and acetylation. The chemical modification can vary greatly, therefore, depending on the ultimate application of the lecithin.
The heating of lecithin containing compositions, in general, is known. Such heating generally takes place in the form of a sterilization step or a drying step.
A few more specific instances of heating a lecithin containing composition include those described in U.S. Pat. No. 4,670,247 and U.S. Pat. No. 4,323,124. The first patent heats a composition containing lecithin to 180.degree. C. for about one minute, and then at lower temperatures for more extended periods of time, in order to crosslink various major materials within the composition. The second patent, i.e., U.S. Pat. No. 4,323,124, injects lecithin with steam into a bore hole so that the lecithin acts as a coating for the rock formation. The injected steam is at a temperature of from 500 to 575.degree. F.
In Japanese Patent Application No. 60-214845, there is disclosed the preparation of a powder for use as an emulsifier in the food industry, primarily for use by confectioners and noodle manufacturers. The method involves heating a mixture of lecithin and starch at a temperature of from the gelatinization temperature of the starch to 140.degree. C. together with water to thereby form a lecithin-starch complex. This complex is then dried and powdered.
The problems encountered upon subjecting lecithin to heat are also recognized in the art, however, and solutions to avoid either using heat or to improve the chemical integrity of the lecithin at higher temperatures have been suggested.
For example, in U.S. Pat. No. 4,479,977, it is disclosed that the loss of chemical integrity by lecithin during heating is well documented. Lecithin is known to darken and give off odors upon heating. These changes are traced to a number of complex reactions between or within the phosphatide molecules. The object of the patent, therefore, is to avoid the decomposition of lecithin and improve its "chemical integrity" at higher temperatures. The solution suggested in the patent is acylating the lecithin in order to make it a heat resistant release agent.
U.S. Pat. No. 4,157,404 discloses a specific lecithin, i.e., yolk lecithin. The patent discloses that yolk lecithin is extremely susceptible to oxidation and therefore, when the yolk lecithin is heat treated at a temperature as high as 60.degree. C. or more under atmospheric pressure, the color of yolk lecithin changes from yellowish orange to brown through yellowish brown. Accordingly, the patent suggests that a heat treatment to remove solvent in order to obtain a yolk lecithin is undesirable. The suggested route, in order to avoid the degradation of the yolk lecithin, is a novel solvent extraction method.
Thus, the two foregoing patents both discuss methods designed to avoid any heat treatment of lecithin. The suggestion is that upon heat treating lecithin, the results are bad and the resulting products are useless and/or undesirable.
While the use of lecithin in various applications is well known, including applications as an emulsifier, and various modifications of lecithin to improve its use in these applications have been suggested, a truly effective yet simple emulsifier based upon lecithin, particularly for water-in-oil emulsions, has heretofore been unknown to the art. The recognition and existence of such a simple, effective and easily obtained emulsifier would certainly benefit the industry and encourage the use of emulsion systems, and particularly water-in-oil emulsion systems.
Accordingly, it is an object of the present invention to provide a simple and easily prepared emulsifier composition which exhibits improved emulsification characteristics.
Yet another object of the present invention is to provide such an emulsifier composition which is particularly effective in stabilizing water-in-oil emulsions.
Still another object of the present invention is to provide a novel, stable water-in-oil emulsion which is comprised of such an emulsifier composition.
Another object of the present invention is to provide a simple, novel process for preparing a stable water-in-oil emulsion.
Yet another object of the present invention is to provide such a process for preparing a water-in-oil emulsion which exhibits good holding capacity with respect to the discontinuous aqueous phase.
These and other objects, as well as the scope, nature and utilization of the invention, will be apparent to those skilled in the art from the following description and the appended claims.